The invention relates to a photographic camera having an interchangeable lens which, by means of an automatic focusing device with a sharpness memory, images on a ground-glass screen an object image which is observable in a view finder of the camera. The camera also has an exposure metering and automatic program exposure control device based on the open-aperture system, and an electronic computing circuit for the determination of the limits of the depth of field of the sharply imaged object by means of the data transmitted from a read-only memory (ROM) or a microprocessor (CPU) of the interchangeable lens to a central unit (C.sup.2 PU), to a focusing control unit and also to the exposure control device.
A photographic camera having automatic exposure and depth-of-field information in the viewfinder is disclosed in German Offenlegungsschrift No. 3,035,568. An electronic computing circuit having a computer which can be switch over to two computer programs for the front and rear limit of depth of field is employed in this camera. The inputs of the computer are connected to signal generators for the set distance, the preselected aperture and the focal length of the particular lens which is employed in each instance. Signal values characterizing the limits of the respective depth of field are present at the output of the computing circuit. These can be fed to the viewfinder, so that the exposure distance and the depth-of-field range are displayed thereon digitally or by means of an LED line, along with the exposure values. For this purpose, it is necessary, after the manual focusing on a definite object and the aperture preselection, to actuate a depth-of-field key. In this case, an exact assessment of the depth-of-field range by observation of the entire ground-glass screen image is not possible.
German Offenlegungsschrift No. 2,755,368 discloses a photographic camera having a device for association and display of the depth-of-field range and lens-focusing values. The device comprises an actual-value generator for the set distance, a memory for the front and rear depth-of-field plane, two computers connected to the memory for the determination of the theoretical aperture number and the theoretical focusing distance, and a comparator for the output signals of the actual-value generator and the second computer. A first display device connected to the output of the comparator responds in the event of coincidence and/or deviation of the output signals of the actual-value generator and the second computer while a second display device, connected to the output of the first computer, is provided for the theoretical aperture number.
After manual focusing on the front and rear depth-of-field plane, respectively, and storage of the respective values, the display device emits a stop signal on actuation of the distance-setting device, when the exact distance is set. This camera does not provide a ground-glass screen display of the limits of the depth of field in the case of automatic focusing.
Finally, photographic cameras having automatic focusing and automatic exposure control according to the method of open-aperture metering (TTL metering) are known, and these cameras have a stop-down key. The stop-down key closes the lens to the working or operational aperture, and can be used for the depth-of-field monitoring of the ground-glass screen image in the viewfinder. At relatively large aperture numbers corresponding to relatively small apertures, a darkening of the ground-glass screen image takes place, and this makes the assessment of the depth of field considerably more difficult.